unstable: for example, the world lines of the dust particles in the Gödel solution have vanishing shear, expansion, and acceleration, but constant vorticity just balancing a constant Raychuadhuri scalar due to nonzero vacuum energy ("cosmological constant").
Kurt Gödel | Gödel | Metric system | United States Metric Board | metric system | Alex Metric | U.S. Metric Association | The Metric Marvels | Performance metric | Metric signature | Metric expansion of space | metric expansion of space | Kerr metric | Kantowski-Sachs metric | Godel's theorem | Gödel's incompleteness theorems | Godel's incompleteness theorem | Gödel metric | Gödel, Escher, Bach | Friedmann–Lemaître–Robertson–Walker metric | Fisher information metric |